Add CLAUDE.md documentation

Agent instructions with Go project structure, auth mechanisms, command
reference, build instructions, and design decisions.

Author: Alexanderamiri

CLAUDE.md

@@ -0,0 +1,62 @@
+# CLAUDE.md — Javabin CLI
+
+Developer CLI for the Javabin platform, written in Go.
+
+## Project Structure
+
+```
+main.go                   Entrypoint — calls cmd.Execute()
+cmd/
+  root.go                 Cobra root command, registers subcommands
+  register.go             Interactive app registration wizard
+  status.go               Project status (costs, ECS services)
+  whoami.go               Show AWS + GitHub identity
+internal/
+  aws/aws.go              AWS SDK helpers (STS, Cost Explorer, ECS)
+  config/config.go        Config directory (~/.javabin/)
+  github/github.go        GitHub API client (token, branches, PRs)
+```
+
+## Dependencies
+
+- `github.com/spf13/cobra` — CLI framework
+- `github.com/aws/aws-sdk-go-v2` — AWS SDK (STS, Cost Explorer, ECS)
+- Go 1.22+
+
+## Authentication
+
+- **GitHub**: Uses `gh auth token` (gh CLI) first, then falls back to `GITHUB_TOKEN` / `GH_TOKEN` environment variables
+- **AWS**: Standard credential chain via `aws-sdk-go-v2/config` (env vars, `~/.aws/credentials`, SSO). Region defaults to `eu-central-1`.
+- **Cognito**: TODO — will add device flow auth against internal Cognito pool when Identity (Phase 1) is implemented. Token will be cached at `~/.javabin/token`.
+
+## Commands
+
+| Command | What it does |
+|---------|-------------|
+| `javabin register` | Interactive wizard — prompts for repo, team, auth, budget; creates a registration PR against `javaBin/registry` via GitHub API |
+| `javabin status` | Shows month-to-date cost (Cost Explorer) and ECS service status. Infers project from git remote or accepts `--project` flag |
+| `javabin whoami` | Shows AWS identity (STS GetCallerIdentity) and GitHub user (gh API) |
+
+## Build and Test
+
+```bash
+go build -o javabin .
+./javabin --help
+```
+
+No tests yet. When adding tests, use standard `go test ./...`.
+
+## Release
+
+Releases are built with GoReleaser on semver tags. Binaries go to GitHub Releases and the Homebrew tap (`javaBin/tap/javabin`).
+
+## Design Decisions
+
+- **No deploy/plan/apply commands** — those run exclusively in CI. The CLI is for registration and status only.
+- **No infrastructure management** — use `app.yaml` and let the platform handle it.
+- **GitHub API directly** (not `go-github` library) — keeps dependencies minimal for a simple REST client.
+
+## Related
+
+- [javaBin/platform](https://github.com/javaBin/platform) — infrastructure the CLI queries
+- [javaBin/registry](https://github.com/javaBin/registry) — where `javabin register` creates PRs